JP2001227384A - Exhaust emission control device for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the air-fuel ratio control accuracy by suppressing the dispersion generated in a target value even if there is dispersion in an air-fuel ratio sensor and an air-fuel ratio control. SOLUTION: When air-fuel ratio control conditions are satisfied, a control means 23 controls the air-fuel ratio of an engine so that the catalyst oxygen carrying quantity becomes a target value. In a case where the air-fuel ratio downstream of the catalyst is near a stoichiometric air amount operation means 25 and 26 calculate the oxygen desorption quantity of the catalyst, when the air-fuel ratio in the upstream of the catalyst is rich, and the oxygen absorption quantity of the catalyst, when the air-fuel ratio in the upstream of the catalyst is lean. Sampling means 27, 28 perform sampling with the oxygen desorption quantity of the catalyst, when the air-fuel ratio downstream of the catalyst is changed from the stoichiomertic air amount to rich, set to the maximum catalyst oxygen desorption quantity, and perform sampling with the oxygen absorption quantity of the catalyst, when the air-fuel ratio in the downstream of the catalyst is changed from the stoichiometric air amount to lean, set to the maximum catalyst absorption quantity oxygen. An operation means 30 calculates the target value based on the average value of the two maximum values.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an engine exhaust purification device.

[0002]

2. Description of the Related Art HC, CO, N which are harmful components in exhaust gas
In order to simultaneously purify Ox with a three-way catalyst (hereinafter simply referred to as “catalyst”), the atmosphere of the catalyst must be a stoichiometric air-fuel ratio (hereinafter simply referred to as “stoichiometric”). Thus, the catalyst is provided with a so-called oxygen storage capability of absorbing insufficient oxygen or desorbing excess oxygen. As a result,
For example, when lean (hereinafter simply referred to as "lean") exhaust is given from a stoichiometric catalyst to a state in which oxygen is not retained (absorbed), excess oxygen is instantaneously absorbed into the catalyst. Until the oxygen holding amount becomes saturated, the catalyst atmosphere is kept stoichiometric. Conversely, when exhaust gas richer than stoichiometric (hereinafter simply referred to as "rich") is given to the catalyst holding oxygen, oxygen in the catalyst is instantaneously desorbed and becomes insufficient in the atmosphere. Oxygen is supplemented. Therefore, the catalyst atmosphere is kept stoichiometric until all the oxygen retained in the catalyst is desorbed.

As described above, since the catalyst has the oxygen storage capacity, the catalyst can compensate for the excess or deficiency of oxygen caused by the temporary air-fuel ratio shift, thereby keeping the catalyst atmosphere stoichiometric. In other words, when the oxygen holding amount of the catalyst reaches the saturation amount or the catalyst does not hold oxygen, it becomes impossible to purify HC, CO, and NOx, and the exhaust emission deteriorates.

[0004] In order to prevent exhaust gas emissions from deteriorating by making full use of the oxygen storage capacity, the amount of excess or deficiency oxygen flowing into the catalyst per predetermined time is calculated. A method has been proposed in which the retained amount is determined and feedback control is performed so that the catalytic oxygen retained amount matches the target value of the catalytic oxygen retained amount (Japanese Patent Laid-Open Nos. 5-195842 and 7-19542).
259602).

[0005]

According to the conventional apparatus, the amount of retained catalyst oxygen at the timing when the exhaust air-fuel ratio downstream of the catalyst shows a lean value is sampled as the maximum amount of retained catalyst oxygen, and the maximum amount of retained catalytic oxygen is sampled. Since the target value is set to の of the amount, the catalyst oxygen holding amount is affected by the variation of the sensor for detecting the exhaust air-fuel ratio upstream or downstream of the catalyst or the variation of other air-fuel ratio control. A large variation occurs in the target value, and the target value cannot be set optimally.

[0006] This will be described with reference to the model diagram of FIG.
To be clear, the O downstream of the catalyst_TwoSensor output is lambda control
During the operation, even in a steady state, the wave changes as shown in FIG._Two
When the sensor output is the slice level LSL and RSL (LSL <
RSL) (for example, t1 to t2 and t
3 to t4), the exhaust air-fuel ratio downstream of the catalyst
It is determined that there is alive. However, in two sections
The air-fuel ratio upstream of the catalyst is different. That is, t1 to t
In section 2, the exhaust air-fuel ratio upstream of the catalyst is rich, whereas
In the section between t3 and t4, the exhaust air-fuel ratio upstream of the catalyst is lean.
is there. Note that O _TwoTouch when sensor output is less than LSL
If the exhaust air-fuel ratio downstream of the medium is lean, O_TwoSensor output
Is higher than RSL, the exhaust air-fuel ratio downstream of the catalyst is rich
It is needless to say that each is determined to be.

In this case, due to variations in the output of the O ₂ sensor, those shown in the figure are from t3 to t4 with respect to the section from t1 to t2.
Section is longer. At this time, in this case, the timing indicating lean is later than that of the O ₂ sensor having no variation. Therefore, according to the conventional device, a value larger than the actual value is calculated as the maximum catalyst oxygen holding amount,
The target value shifts to a side larger than the optimum value. Conversely, although not shown due to variations in the O ₂ sensor, t1 to t
When the interval from t3 to t4 is shorter than the interval from _{2, the} leaning timing is earlier than that of the O ₂ sensor having no variation. According to the conventional apparatus, a value smaller than the actual value is the maximum catalyst oxygen retention. It is calculated as a quantity, and the target value is shifted to a side smaller than the optimum value.

Although the variation occurring in the section between t3 and t4 has been described, the same applies to the case where variation occurs between t1 and t2.

Therefore, the present invention provides a method for controlling the exhaust air-fuel ratio upstream of the catalyst to be lean (t3 to t4) and rich (t3) when the exhaust air-fuel ratio downstream of the catalyst is near the stoichiometric ratio.
1 to t2), the maximum value (the maximum value of the catalyst oxygen desorption amount when the exhaust air-fuel ratio upstream of the catalyst is lean, and the maximum value of the catalyst oxygen absorption amount when the exhaust air-fuel ratio upstream of the catalyst is rich). Value), and setting a target value based on the average value, thereby suppressing variations in the target value even if the air-fuel ratio sensor and the air-fuel ratio control vary, thereby improving the air-fuel ratio control accuracy. With the goal.

[0010]

According to a first aspect of the present invention, as shown in FIG. 11, a catalyst 21 having an oxygen holding capacity disposed in an exhaust passage of an engine and an exhaust air-fuel ratio downstream of the catalyst 21 are stoichiometric. When the air-fuel ratio control condition is satisfied, the means 22 for calculating the catalyst oxygen holding amount based on the excess / deficiency oxygen amount per predetermined time upstream of the catalyst when the catalyst oxygen holding amount is equal to the target value Means 23 for controlling the air-fuel ratio of the engine so that the target air-fuel ratio downstream of the catalyst 21 is close to stoichiometric and the catalyst 21 upstream Means 25 for calculating the amount of catalyst oxygen desorbed when the exhaust air-fuel ratio is rich, and when the exhaust air-fuel ratio downstream of the catalyst 21 is near stoichiometric and the exhaust air-fuel ratio upstream of the catalyst 21 is lean, It means 26 for calculating a medium oxygen absorption amount
Means 27 for sampling the amount of catalyst oxygen desorbed when the exhaust air-fuel ratio downstream of the catalyst 21 changes from stoichiometric to rich, as the maximum amount of catalyst oxygen desorbed;
Means 28 for sampling the amount of catalytic oxygen absorption when the exhaust air-fuel ratio at one downstream changes from stoichiometric to lean as a maximum catalytic oxygen absorption amount, and an average of these two maximum catalytic oxygen desorption amounts and the maximum catalytic oxygen absorption amount Means 2 for calculating values
9 and means 30 for calculating the target value based on the average value.

A second invention, as shown in FIG. 12, is a catalyst provided in an exhaust passage of an engine and having an oxygen holding ability, wherein at least one of a component having a high rate of oxygen absorption or desorption and a component having a low rate of oxygen desorption is provided. A catalyst 41 containing two components, and a component having a high rate of oxygen absorption or desorption based on the excess / deficient oxygen amount per predetermined time upstream of the catalyst when the exhaust air-fuel ratio downstream of the catalyst 41 is near stoichiometric. a means 42 for calculating a catalytic oxygen holding amount HOSC _n by, during the establishment of the air-fuel ratio control condition, the oxygen absorbing or oxygen decatalyzed oxygen holding amount rate by fast component of the release HOSC _n at that time
Means 43 for controlling the air-fuel ratio of the engine so as to be a target value only for a component having a high rate of oxygen absorption or oxygen desorption, and means 44 for setting the target value.
The catalyst 41 downstream of the exhaust air-fuel ratio is in the vicinity of the stoichiometric and when the exhaust air-fuel ratio of the catalyst 41 upstream of the rich, computing the oxygen absorbing or oxygen desorption catalyst oxygen desorption amount HOSCR _n rate by fast component of Means 45 and the catalyst 4
1 the downstream air-fuel ratio is near stoichiometric and the catalyst 4
1. When the upstream exhaust air-fuel ratio is lean, the catalytic oxygen absorption amount HO due to the component having a high oxygen absorption or oxygen desorption speed.
A means 46 for calculating the SCL _n, the oxygen absorbing or oxygen desorption rate of oxygen absorption of the catalyst oxygen desorption amount according to the fast component or oxygen removal when the air-fuel ratio of exhaust gas downstream the catalyst 41 is changed to the rich from the stoichiometric Means 47 for sampling as the maximum amount of catalytic oxygen desorbed by the component having a high release speed
When the exhaust air-fuel ratio downstream of the catalyst 41 changes from stoichiometric to lean, the amount of catalyst-absorbed oxygen due to the component having a high rate of oxygen absorption or desorption is increased by the component having a high rate of oxygen absorption or desorption. Means 48 for sampling as the amount of catalytic oxygen absorbed, and means 49 for calculating the average value of the maximum amount of desorbed catalytic oxygen and the maximum amount of absorbed catalytic oxygen.
Means 5 for calculating the target value based on the average value
It consists of 0.

In a third aspect of the present invention, the component having a high rate of oxygen absorption or oxygen desorption in the second aspect is a catalytic metal.

According to a fourth aspect, in the second aspect, the component having a low rate of oxygen absorption or oxygen desorption is an oxygen absorption aid.

According to a fifth aspect of the present invention, in any one of the second to fourth aspects, the means for calculating the amount of catalytic oxygen desorbed by the component having a high rate of oxygen absorption or oxygen desorbing is provided.
5 means for integrating the amount of catalytic oxygen desorbed per predetermined time by a component having a high rate of oxygen absorption or oxygen desorbing,
The means 46 for calculating the amount of catalytic oxygen absorbed by the component having a high rate of oxygen absorption or oxygen desorption is means for integrating the amount of catalytic oxygen absorbed per predetermined time by the component having a high rate of oxygen absorption or oxygen desorption. .

According to a sixth aspect of the present invention, in the fifth aspect, the amount of catalytic oxygen desorbed per predetermined time due to the component having a high oxygen absorption or oxygen desorption rate and the component having a high oxygen absorption or oxygen desorption rate per unit time are provided. The catalyst oxygen absorption amount per predetermined time is the same fixed value.

According to a seventh aspect, in the fifth aspect, the amount of catalytic oxygen desorbed per predetermined time by the component having a high oxygen absorption or desorbing rate is determined based on the amount of oxygen deficiency per predetermined time upstream of the catalyst. Further, the amount of catalyst oxygen absorbed per predetermined time by the component having a high rate of oxygen absorption or oxygen desorption is calculated based on the excess oxygen amount per predetermined time upstream of the catalyst.

According to an eighth aspect of the present invention, in any one of the first to seventh aspects, a sensor (for example, a wide-range air-fuel ratio sensor) for detecting an excess / deficiency oxygen amount per predetermined time upstream of the catalyst, Means for correcting a shift shift occurring in the sensor output, and sampling the maximum catalyst oxygen desorption amount and the maximum catalyst oxygen absorption amount when the number of corrections of the shift shift or the integrated value of the correction values becomes a predetermined value or more. Do not allow.

In a ninth aspect, in any one of the first to seventh aspects, when the catalyst is not in an active state, sampling of the maximum catalytic oxygen desorption amount and the maximum catalytic oxygen absorption amount is not permitted.

[0019]

The variation or other air-fuel ratio control of the variation of the air-fuel ratio sensor according to the present invention (e.g. wide-range air-fuel ratio sensor or O ₂ sensor), the exhaust gas air-fuel ratio downstream of the catalyst is in the vicinity of the stoichiometric and of the catalyst upstream exhaust air Even if there is a difference in length between the section when the fuel ratio is rich and the section when the exhaust air-fuel ratio downstream of the catalyst is near stoichiometric and the exhaust air-fuel ratio upstream of the catalyst is lean, these two According to the first and second inventions corresponding to the difference in the section length, when the exhaust air-fuel ratio downstream of the catalyst is close to stoichiometric and the exhaust air-fuel ratio upstream of the catalyst is rich, and when the exhaust air-fuel ratio downstream of the catalyst is stoichiometric. When the exhaust air-fuel ratio near the catalyst is lean and the exhaust air-fuel ratio upstream of the catalyst is lean, the maximum value is different (when the exhaust air-fuel ratio downstream of the catalyst is near stoichiometric and the exhaust air-fuel ratio upstream of the catalyst is rich, the maximum catalyst oxygen desorption amount , When the exhaust air-fuel ratio downstream of the medium is near stoichiometric and the exhaust air-fuel ratio upstream of the catalyst is lean, the maximum catalyst oxygen absorption amount is calculated, and the target value is calculated based on the average of the two maximum values. Therefore, due to variations in the air-fuel ratio sensor and other variations in the air-fuel ratio control, the section where the exhaust air-fuel ratio downstream of the catalyst is near stoichiometric and the exhaust air-fuel ratio upstream of the catalyst is rich, Even if the exhaust air-fuel ratio downstream of the catalyst is near the stoichiometric ratio and the length of the exhaust air-fuel ratio upstream of the catalyst is different from the section where the exhaust air-fuel ratio is lean, the variation in the target value can be suppressed. The air-fuel ratio control accuracy can be improved.

In the second, third, fourth, and fifth aspects of the present invention, only the amount of catalyst oxygen retained by a component having a high rate of oxygen absorption or oxygen desorption is calculated, and the calculated value is calculated based on the oxygen absorption or oxygen desorption. Since the air-fuel ratio is controlled so that it becomes the target value for only the component with a high velocity, the convergence to the target value is accelerated, and the influence of the component with a low oxygen absorption rate that does not contribute to the exhaust performance in a short time is thereby affected. Can be eliminated.

Variations in the air-fuel ratio sensor and other variations in the air-fuel ratio control include a section in which the exhaust air-fuel ratio downstream of the catalyst is near stoichiometric and an exhaust air-fuel ratio upstream of the catalyst is rich, and a section in which the exhaust air-fuel ratio downstream of the catalyst is rich. When the fuel ratio is close to the stoichiometric ratio and the air-fuel ratio upstream of the catalyst is lean, it appears as a difference in length. Since the separation amount and the catalyst oxygen absorption amount per predetermined time can be the same fixed value, the calculation of the target value can be simplified according to the sixth invention.

According to the seventh aspect, when the exhaust air-fuel ratio downstream of the catalyst is close to the stoichiometric ratio and the exhaust air-fuel ratio upstream of the catalyst is rich, even if the degree of the rich changes, the downstream of the catalyst can be reduced. When the exhaust air-fuel ratio is near the stoichiometric ratio and the exhaust air-fuel ratio upstream of the catalyst is lean, even if the degree of lean changes, the maximum catalyst oxygen desorption amount due to the component with a high oxygen absorption or desorption speed is It is possible to accurately calculate the maximum amount of catalytic oxygen absorbed by a component having a high rate of oxygen absorption or oxygen desorption.

When a shift shift occurs in the sensor output,
If the number of shift shift corrections or the integrated value of the correction values exceeds a predetermined value, the sensor may be faulty. Therefore, sampling of the maximum value (the maximum amount of catalytic oxygen desorption and the maximum amount of catalytic oxygen absorption) in such a state should be performed. According to the eighth invention, which is not permitted, it is possible to suppress the variation of the maximum value (target value).

When the catalyst is not in an active state, it is difficult to desorb oxygen from the catalyst or to absorb oxygen into the catalyst. Therefore, the maximum value (the maximum catalyst oxygen desorption amount and the maximum catalyst oxygen absorption amount) in this state is low. According to the ninth invention in which sampling is not allowed,
Variation of the maximum value can be suppressed.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, reference numeral 1 denotes an engine main body. A fuel injection valve 7 is provided in an intake passage 8 at a position downstream of an intake throttle valve 5 and is operated by an injection signal from a control unit 2. Fuel is injected and supplied into the intake air so that a predetermined air-fuel ratio is obtained according to conditions. The control unit 2 includes a rotation speed signal from the crank angle sensor 4, an intake air amount signal from the air flow meter 6, a water temperature sensor 1,
1, the fuel injection amount Tp from which the basic air-fuel ratio can be obtained is determined, and the fuel injection amount Ti is calculated by performing various corrections while determining the operating state based on these. By converting this into an injection signal, the fuel injection amount is controlled.

A catalyst 10 is provided in the exhaust passage 9. The catalyst 10 reduces NOx in exhaust gas and oxidizes HC and CO with maximum conversion efficiency during stoichiometric operation. At that time, the catalyst 10 keeps the catalyst atmosphere stoichiometric by supplementing the excess or deficiency of oxygen caused by the temporary air-fuel ratio deviation with the oxygen storage capacity (oxygen holding capacity).

The oxygen holding amount of the catalyst 10 is

[0028]

[Equation 1] Oxygen holding amount = {displacement amount × (over / under oxygen concentration upstream of the catalyst−over / under oxygen concentration at the downstream of the catalyst)}.

Here, the “over-deficient oxygen concentration” in the equation (1) is:
As shown in FIG. 4 to be described later, the air-fuel ratio at that time is converted into an oxygen concentration, with the stoichiometric value as the reference zero. For example, when the air-fuel ratio is lean, the oxygen concentration in the stoichiometric oxygen is excessive, so the excess / deficient oxygen concentration is a positive value, and when the air-fuel ratio is rich, the oxygen concentration in the stoichiometric oxygen is insufficient. Is the value of

In a general engine, air-fuel ratio feedback control (hereinafter referred to as "lambda control") is performed based on the output of an air-fuel ratio sensor upstream of the catalyst so that the average air-fuel ratio of the exhaust gas coincides with the stoichiometric ratio. Is almost stoichiometric (constant), and at this time, the excess / deficiency oxygen concentration downstream of the catalyst becomes almost zero.

Therefore, while the air-fuel ratio downstream of the catalyst is stoichiometric, the excess / deficiency oxygen concentration downstream of the catalyst is set to zero in the above equation (1).

[0032]

## EQU2 ## The oxygen holding amount is calculated according to the following equation: Oxygen holding amount = Σ (displacement amount × over / under oxygen concentration upstream of the catalyst).

The prior application (Japanese Patent Application No. 10-295110)
According to the experimental results, it was found for the first time that oxygen was absorbed by the catalyst even after the air-fuel ratio downstream of the catalyst became lean.

To explain this finding, the air-fuel ratio of the exhaust gas is set to 1
FIG. 2 shows the results (experimental results) of measuring the air-fuel ratio before and after the catalyst when switching from about 3 rich to about 16 lean.
Shown in In the figure, in the section A, the speed at which the catalyst absorbs oxygen is high, and the air-fuel ratio upstream of the catalyst (“FA /
F) is lean, the excess air flowing into the catalyst is absorbed by the catalyst, so that the air-fuel ratio downstream of the catalyst (indicated by "RF / A" in the figure) is lean. No (indicates stoichiometry). On the other hand, when moving to the section B,
All of the excess oxygen flowing in is not absorbed by the catalyst,
The air-fuel ratio downstream of the catalyst is lean. That is, even in the section B where the air-fuel ratio downstream of the catalyst is lean,
Although the rate of absorption is slow, oxygen (or an oxide such as NO) is absorbed by the catalyst.

To explain this further, the illustrated one is a noble metal supported on a catalyst (hereinafter simply referred to as “catalytic metal”).
In addition to the above, an additive (hereinafter simply referred to as "oxygen absorption aid") for assisting oxygen absorption is provided. in this case,
Catalytic metals (eg, platinum and rhodium) absorb oxygen by adsorbing oxygen in a molecular state, referred to as physical adsorption, whereas oxygen-absorbing aids (eg, cerium oxide, barium, base metals) There is a difference in that oxygen is absorbed in the form of a compound by chemical bonding. Due to such a difference in the method of oxygen absorption (also in the case of oxygen desorption), there is a fast component and a slow component in the rate of oxygen absorption. I think that the. It should be noted that although the term "adsorption" is more accurate for a catalytic metal, the difference here is only the difference between the rate of oxygen adsorption and the rate of oxygen absorption. Therefore, absorption is also used for the catalytic metal.

Therefore, in FIG. 2, the amount of catalyst oxygen retained when the air-fuel ratio downstream of the catalyst changes from stoichiometric to lean is defined as the maximum amount of catalytic oxygen retained by the catalytic metal, and thereafter the amount of oxygen absorbed by the oxygen absorption aid. Is the amount of catalyst oxygen retained by the oxygen absorption aid, the amount of oxygen absorbed by the catalyst during fuel cut or lean clamp (hereinafter represented by fuel cut) is the maximum amount of catalyst oxygen retained by the catalyst metal. The amount of catalyst oxygen retained by the oxygen absorption aid is added.

However, according to the conventional apparatus, the catalyst oxygen holding amount at the timing when the air-fuel ratio sensor downstream of the catalyst indicates lean is defined as the maximum catalyst oxygen holding amount, and の of the maximum catalyst oxygen holding amount is set to the target value. Therefore, the amount of oxygen held in the section B (the amount of catalyst oxygen held by the oxygen absorption auxiliary) is ignored. For this reason, it is considered that an error occurs when the fuel cut is canceled and the process returns to the air-fuel ratio control for keeping the catalyst oxygen holding amount at the target value.

Therefore, during a period in which the air-fuel ratio downstream of the catalyst is lean, such as when the fuel is cut, the catalyst oxygen holding amount including the oxygen holding amount absorbed by the catalyst by the oxygen absorption auxiliary is calculated, and the catalyst oxygen holding amount is calculated. The target value was set to 1/2 of the value obtained by adding the maximum catalytic oxygen holding amount by the metal to the maximum catalytic oxygen holding amount by the metal, and also included the oxygen holding amount absorbed by the catalyst by the oxygen absorbing auxiliary agent. By performing the air-fuel ratio control so that the catalyst oxygen holding amount becomes the target value, it is possible to prevent an error from occurring when returning to the air-fuel ratio control that keeps the catalyst oxygen holding amount at the target value after a fuel cut or high output. It is conceivable to prevent it.

However, according to an experiment, the rate of oxygen absorption or desorption of oxygen by the oxygen-absorbing auxiliary agent is very slow (very little controllable) compared to the rate of oxygen absorption or desorption of oxygen by the catalytic metal. However, if the target value is set based on the maximum value of the oxygen holding amount absorbed by both the catalyst metal and the oxygen absorption auxiliary, it takes a very long time to return the catalyst oxygen holding amount to the target value. It was found that the manipulated variable of the air-fuel ratio remained on one of the rich side and the lean side, and exhaust harmful components could not be reduced sufficiently. That is, even if the amount of catalyst oxygen retained by the oxygen absorption aid is taken into the target value, it does not contribute to the exhaust performance in a short time.

Therefore, when the exhaust air-fuel ratio downstream of the catalyst is near the stoichiometric ratio, the control unit 2 calculates only the amount of catalyst oxygen retained by the catalyst metal based on the amount of excess / deficient oxygen per predetermined time upstream of the catalyst. When the fuel ratio control condition is satisfied, the air-fuel ratio of the engine is controlled such that the amount of catalyst oxygen retained by the catalyst metal at that time becomes a target value for only the catalyst metal.

The control performed by the control unit 2 will be described with reference to the flowchart of FIG.

It should be noted that, based on the air-fuel ratio signal from the wide-range air-fuel ratio sensor 3 upstream of the catalyst, the control unit 2
The lambda control is performed under the lambda control condition (predetermined air-fuel ratio control condition).

Here, in detail, the lambda control calculates the air-fuel ratio feedback correction coefficient α so that the average value of the exhaust air-fuel ratio upstream of the catalyst 10 becomes stoichiometric, and the basic injection amount Tp is calculated using the correction coefficient α. This is the control for correction.

However, since the sensor 3 upstream of the catalyst is a wide-range air-fuel ratio sensor, proportional component = proportional gain × ΔA / F, integral component = integral gain × ΣΔA / F / T2, where ΔA / F: empty Fuel ratio deviation (= actual air-fuel ratio-stoichiometric) T2: integration interval (elapsed time since the sign of the air-fuel ratio deviation is inverted), a proportional component and an integral component are obtained by the following equation, and the sum of them is α
A general proportional-integral control (= proportional component + integral component) is performed.

The process shown in FIG. 3 is executed at regular intervals (for example, every 10 ms) regardless of the lambda control.

First, in S1, it is determined whether or not the catalyst 10 is activated according to conditions such as the cooling water temperature. If the catalyst 10 has not been activated, the oxygen storage capacity of the catalyst 10 does not work, so the current process is terminated.

If the catalyst 10 has been activated, the process proceeds to S2, where the wide-range air-fuel ratio sensor upstream of the catalyst (“FA / F
Sensor), the excess / deficiency oxygen concentration FO2 in the exhaust gas is obtained by searching the table of FIG.
Read this.

As shown in FIG. 4, the excess / deficient oxygen concentration FO2 in the exhaust gas is a value obtained by converting the air-fuel ratio at that time to an oxygen concentration with a stoichiometric value of zero as a reference.
Therefore, for example, when the air-fuel ratio is lean, the oxygen concentration of the stoichiometric oxygen is excessive, and thus FO2 is a positive value. When the air-fuel ratio is rich, the oxygen concentration of the stoichiometric oxygen is insufficient. Becomes

As shown in FIG. 4, a wide range air-fuel ratio sensor (abbreviated as "A / F sensor" in the figure) has a measurable range. Therefore, when the fuel is cut, the air-fuel ratio becomes lean outside the measurement range, and the air-fuel ratio at the time of the fuel cut (therefore, the excess / deficient oxygen concentration at the time of the fuel cut) cannot be obtained. However, the required air-fuel ratio (hereinafter simply referred to as the required air-fuel ratio) when combusting the air-fuel mixture is determined. If a wide-range air-fuel ratio sensor that covers the required air-fuel ratio is used, lean outside the measurement range will always require a fuel cut. Therefore, when the wide-range air-fuel ratio sensor that only covers the required air-fuel ratio indicates a lean outside the measurement range, the excess / deficiency oxygen concentration FO2 at that time is set to a value relative to the atmosphere as shown in FIG. 9%). FIG. 5 shows the relationship shown in FIG. 4 as a table.

In this manner, even if the wide-range air-fuel ratio sensor only covers the required air-fuel ratio, the excess / deficient oxygen concentration FO2 at the time of fuel cut can be obtained.

Returning to FIG. 3, in S3, the output of the O ₂ sensor downstream of the catalyst (abbreviated as “R-O 2 sensor” in the figure, the same in FIG. 6 described later) is compared with a predetermined value. When it is determined that the output of the O ₂ sensor is equal to or more than a predetermined value (rich), it is determined that the catalyst oxygen holding amount has run out and the catalyst 10 cannot maintain the air-fuel ratio downstream of the catalyst at stoichiometry. HOSC _n is reset to zero. Here, “n” added to the HOSC represents the current value. On the other hand, “n−1” is added to the previous value. This code is also used in FIG. 6 described later.

On the other hand, if the O ₂ sensor output is not equal to or more than the predetermined value, the process proceeds to S5, and it is checked whether the O ₂ sensor output is equal to or less than the predetermined value (lean). If it is not lean (that is, the air-fuel ratio downstream of the catalyst is stoichiometric), it is determined that the catalyst 10 has absorbed the air-fuel ratio fluctuation upstream of the catalyst, and the process proceeds to S6.

Here, when the process proceeds to S6, there are two cases, that is, when the lambda control is performed and when the lambda control is not performed. In both cases, the air-fuel ratio downstream of the catalyst becomes stoichiometric. It is when you are.

In S6,

[0055]

HOSC _n = HOSC _n-1 + a × FO2 × Q × t, where HOSC _n : current calculated value, HOSC _n-1 : previous calculated value, a: constant (value for unit conversion is including), FO2: deficiency oxygen concentration, Q: substituting the exhaust flow rate (intake air flow rate), t: calculation cycle time (10 ms), wherein the after S7 computed catalytic oxygen holding amount HOSC _n catalytic metal move on.

Here, FO2 of the second term on the right side of the equation (3)
× Q × t is per operation cycle time (per predetermined time)
Is the amount of oxygen in excess or deficiency.
Calculation speed by multiplying by a constant a that determines the speed of
Adsorbed by catalytic metal per hour
Calculate the amount of desorbed oxygen, and calculate this as the previous value HOSC_{n- 1}
To the air-fuel ratio downstream of the catalyst.
The amount of catalytic oxygen retained by the catalytic metal for a period of time
It is.

Further describing the second term on the right side of the above equation (3), the excess / deficiency oxygen amount per operation cycle time is an expression when the excess / deficiency of oxygen centering on stoichiometry is observed. In other words, when the exhaust air-fuel ratio upstream of the catalyst is lean, the second term on the right side of Equation 3 indicates the amount of oxygen retained per operation cycle time by the catalyst metal, and when the exhaust air-fuel ratio upstream of the catalyst is rich. The constant a in the second term indicates the amount of oxygen desorbed per operation cycle time from the catalyst metal, and the rate of oxygen absorption on the side where oxygen is excessive or the rate of oxygen desorption on the side where oxygen is insufficient Has been established.

When the air-fuel ratio downstream of the catalyst becomes lean in S5, the process skips S6 and proceeds to S7.

At S7, a lambda control (in the figure, "λ
Abbreviated as “con”). The lambda control condition is the same as the conventional one, and when the wide area air-fuel ratio sensor 3 upstream of the catalyst is activated or the like, lambda control is started. In addition, the lambda control is clamped (stopped) at the time of fuel cut or high engine load.

If the lambda control is being performed, the process proceeds to the PID control after S8. If the lambda control is not being performed, the process after S8 is skipped. In other words, the calculation of the catalyst oxygen holding amount HOSC _n by the catalyst metal is performed continuously as long as it is after the activity of the catalyst, the calculated catalyst oxygen holding amount HOSC _n feedback control to match the target value (the catalytic oxygen holding amount of the catalyst metal The air-fuel ratio control for achieving the target value for only the catalyst metal is limited to the case where the lambda control is performed.

[0061] In S8, the difference (deviation) HOSCs _n the catalytic oxygen holding amount of the catalyst metal HOSC _n and catalytic oxygen holding amount of the target value (half of the maximum catalytic oxygen holding amount HOSCy by catalytic metal)

[0062]

Equation 4] After calculation by equation _{HOSCs n = HOSC n -HOSCy × 1} /2, in S9, S10, S11

[0063]

Equation 5] Hp = proportional gain × HOSCs _n, Hi = integral gain × ΣHOSCs _n / T, Hd = differential gain _{× (HOSCs n -HOSCs n-1} ) /
t, where: T: integration interval (elapsed time since the sign of the deviation of the catalyst oxygen holding amount is reversed), t: operation cycle time (10 ms), and the proportional amount of feedback amount Hp, integral amount Hi and The differential components Hd are calculated, and the sum of these values is set as the fuel correction amount H (feedback amount) in S12, and the process of FIG. 3 ends.

Using the fuel correction amount H obtained in this way, in a flow (not shown), for example,

[0065]

[Mathematical formula-see original document] Ti = Tp * TFBYA * [alpha] * H * 2 + Ts, where Tp: basic injection pulse width, TFBYA: target equivalence ratio, α: air-fuel ratio feedback correction coefficient, Ts: invalid pulse width, sequential injection Fuel injection pulse width T
i is calculated. And, for every two cylinders of the engine,
Times, the time of Ti at a predetermined injection timing, the fuel injection valve 7
Is opened, and fuel is injected and supplied into the intake pipe.

Here, Tp, TFBYA,
α and Ts are the same as before. For example, α = 1.0 during fuel cut and TFBYA =
1.0. Ts is a correction amount of the injection pulse width according to the battery voltage.

As described above, in this embodiment, only the amount of catalyst oxygen retained by the catalyst metal (a component having a high rate of oxygen absorption or oxygen desorption) is calculated, and the calculated value is set as a target value for only the catalyst metal. Control of the air-fuel ratio, the convergence to the target value is accelerated, thereby eliminating the effect of oxygen absorption aids (components with slow oxygen absorption or oxygen desorption) that do not contribute to short-term exhaust performance it can.

If the target value is の of the maximum amount of catalytic oxygen retained by the catalytic metal, overflow of the amount of catalytic oxygen retained on the lean side and lack of the amount of catalytic oxygen retained on the rich side are unlikely to occur. Sufficient conversion performance of the catalyst can be maintained.

[0069] Now, the wide-range air-fuel ratio sensor and the catalyst downstream O ₂ sensor variations, or other air-fuel ratio control of the variation of the catalyst upstream exhaust air-fuel ratio downstream of the catalyst is in the vicinity of the stoichiometric and the catalyst upstream of the exhaust air Experiments have shown that the section when the fuel ratio is rich and the section when the exhaust air-fuel ratio downstream of the catalyst is near stoichiometric and the exhaust air-fuel ratio upstream of the catalyst are lean differ in length. In the control unit 2, when the exhaust air-fuel ratio downstream of the catalyst is near stoichiometric and the exhaust air-fuel ratio upstream of the catalyst is rich, the exhaust air-fuel ratio downstream of the catalyst is near stoichiometric and the exhaust air-fuel ratio upstream of the catalyst is low. Separate maximum values for lean and maximum (when the exhaust air-fuel ratio downstream of the catalyst is near stoichiometric and the exhaust air-fuel ratio upstream of the catalyst is rich, the maximum Medium oxygen desorption amount, exhaust air-fuel ratio downstream of the catalyst is in the vicinity of the stoichiometric and maximum catalytic amount of oxygen absorbed by the catalyst metal when the exhaust air-fuel ratio upstream of the catalyst is lean)
Is calculated, and a target value is set based on the average value.

The control performed by the control unit 2 will be described with reference to the flowchart of FIG.

FIG. 6 is for calculating the maximum catalyst oxygen holding amount HOSCy by the catalyst metal, and is executed at regular intervals (for example, every 10 ms).

In S21, the excess / deficiency oxygen concentration FO2 in the exhaust gas is read in the same manner as in S2 of FIG.

In step S22, permission conditions for calculating the maximum catalyst oxygen holding amount HOSCy by the catalyst metal are checked. When the permission condition is satisfied (when a permission flag described later is 1), S
Proceed to 23 or later.

S23 to S27 are portions for determining which of the following five cases by comparing the O ₂ sensor output (current value, previous value) with the rich side slice level RSL and the lean side slice level LSL. is there.

<1> When the air-fuel ratio downstream of the catalyst is stoichiometric and the air-fuel ratio upstream of the catalyst is lean, <2> When the air-fuel ratio downstream of the catalyst is stoichiometric and the air-fuel ratio upstream of the catalyst is rich,
<3> timing when the air-fuel ratio downstream of the catalyst changes from stoichiometric to lean, <4> timing when the air-fuel ratio downstream of the catalyst changes from stoichiometric to <5> otherwise (when the air-fuel ratio downstream of the catalyst changes from rich to When the stoichiometric timing and the air-fuel ratio downstream of the catalyst change from lean to stoichiometric), the above cases <1> to <5> are further associated with the waveform diagram of FIG. Is, for example, a section from t3 to t4, <2> is, for example, a section from t1 to t2, <3> is, for example, timing at t4, <4> is, for example, timing at t2, and <5> is, for example, t1 and t.
This is timing 3.

Returning to FIG. 6, in the case of the above <1> (when the O ₂ sensor output is less than RSL or more than LSL and the O ₂ sensor output is decreasing), the process proceeds from S23, S24, S25 to S29, Equation similar to the above equation (3),

[0077]

HOSCL _n = HOSCL _n-1 + aL × FO2 × Q × t, where HOSCL _n : current calculated value, HOSCL _n-1 : previous calculated value, aL: constant (value for unit conversion is FO2: excess and deficiency oxygen concentration, Q: exhaust flow rate (substituted by intake air flow rate), t: operation cycle time (10 ms), and catalyst in which the air-fuel ratio upstream of the catalyst is lean according to the following formula: after calculating the catalyst oxygen absorption amount HOSC _n by metal ends the current process.

Here, FO2 in the second term on the right side of the equation (8)
× Q × t is per operation cycle time (per predetermined time)
Is multiplied by a constant aL which determines the rate of oxygen absorption, to calculate the amount of oxygen absorbed by the catalyst metal per calculation cycle time, and add this to the previous value HOSCL _n-1 . As a result, the amount of catalyst oxygen absorbed by the catalyst metal when the air-fuel ratio upstream of the catalyst is lean while the air-fuel ratio downstream of the catalyst is stoichiometric is determined.

However, the constant aL in equation (8) is the same value as the constant a in equation (3). Here, a code (HOSC _{n of the} equation (3) and HO in the equation (8) are distinguished from the equation (3).
SCL _n ) and the name (catalyst oxygen absorption amount in equation 8 with respect to the catalytic oxygen holding amount in equation 3) are different, and therefore, different signs are used for the constants.

In the case of the above <2> (when the O ₂ sensor output is RS
If the value is less than L or more than LSL and the output of the O ₂ sensor is increased), the process proceeds from S23, S24, S25 to S28,
Equation similar to the above equation (3),

[0081]

HOSCR _n = HOSCR _n-1 + aR × FO2 × Q × t, where HOSCR _n : current calculated value, HOSCR _n-1 : previous calculated value, aR: constant (value for unit conversion FO2: excess and deficiency oxygen concentration, Q: exhaust gas flow rate (substituted by intake air flow rate), t: calculation cycle time (10 ms), catalyst with rich air-fuel ratio upstream of the catalyst after calculating the catalyst oxygen desorption amount HOSC _n by metal ends the current process.

Here, FO2 in the second term on the right side of the equation (7)
× Q × t is per operation cycle time (per predetermined time)
The amount of oxygen desorbed from the catalyst metal per operation cycle time is calculated by multiplying the oxygen deficit by a constant aR that determines the rate of oxygen desorption, and this is added to the previous value HOSCR _n-1 . By doing so, the amount of catalyst oxygen desorbed by the catalyst metal in a state where the air-fuel ratio upstream of the catalyst is rich while the air-fuel ratio downstream of the catalyst is stoichiometric is determined.

However, the constant aR in equation (7) is the same value as the constant aL in equation (6).

On the other hand, in the case of the above <3> (when the O ₂ sensor output is lower than LSL and the previous O ₂ sensor output is higher than LSL), the process proceeds from S23 and S24 to S27, and the catalyst of the catalyst metal at that time is used. the amount of oxygen absorbed HOSCL _n together put in maximum catalytic oxygen absorption amount LMAX catalytic metal, the process proceeds after S34 resets the catalytic oxygen absorption amount HOSCL _n by the catalyst metal to zero in S33 to prepare for the next processing. Similarly, in the case of the above <4> (when the O ₂ sensor output is equal to or more than RSL and the previous O ₂ sensor output is RSL
If it is less than), the process proceeds from S23 and S26 to S30, in which the amount of catalyst oxygen desorbed by the catalyst metal HOSC
With add R _n maximizing catalytic oxygen desorption amount RMAX catalytic metal, the process proceeds after S34 resets the catalytic oxygen desorption amount HOSCR _n by the catalyst metal to zero in S31 to prepare for the next processing.

In S34, a simple average value AVE (= (LMAX + RMAX) / 2) of these two maximum values is calculated. In this case, the average value AVE, which is the calculated value for each time, fluctuates. In order to avoid the influence of this fluctuation, a weighted average value RAVE _n of this average value AVE is calculated in S35.

[0086]

[Mathematical formula-see original document] RAVE _n = AVE * G + RAVE _n-1 * (1-G), where RAVE _n : current calculated value, RAVE _n-1 : previous calculated value, G: weighted average coefficient Then, in S36, this value is set as the maximum catalyst oxygen holding amount HOSCy by the catalyst metal.

The maximum catalytic oxygen holding amount H by this catalytic metal
OSCy is stored in a memory (RAM), and is read and used in S8 in the above-described flow of FIG.

Here, the operation when the maximum catalyst oxygen holding amount HOSCy by the catalyst metal is set according to the present embodiment will be described with reference to FIG. 7 again.
Due to the variation of the _two sensors, the exhaust air-fuel ratio downstream of the catalyst is lower than that of the stoichiometric air-fuel ratio in the interval (t1 to t2) when the exhaust air-fuel ratio downstream of the catalyst is near stoichiometric and the exhaust air-fuel ratio upstream of the catalyst is rich. The interval (interval between t3 and t4) when the exhaust air-fuel ratio is near and upstream of the catalyst is lean is longer.

In this case, according to the conventional apparatus, since the timing of indicating lean is later than the output of the O ₂ sensor without variation, a value larger than the actual value is calculated as the maximum catalyst oxygen holding amount, and the target value is set to the optimum value. Offset to the larger side.

On the other hand, also in this embodiment, t3
O with no variation in the section from t4 to t4 _TwoThan the sensor output
Lean timing is delayed, so it is larger than the actual value.
Is the maximum catalytic oxygen absorption LMAX by the catalytic metal.
Is calculated.

However, in the section between t1 and t2, O ₂
Since there is no variation in the sensor output, the rich timing is not delayed, and a value equivalent to the actual value is calculated as the maximum catalytic oxygen desorption amount RMAX by the catalytic metal. As a result, RMAX has a smaller value than LMAX.

Here, in order to facilitate comparison between the conventional apparatus and the present embodiment, if the maximum catalytic oxygen absorption amount LMAX in the present embodiment is assumed to be substantially equal to the maximum catalytic oxygen holding amount of the conventional apparatus, the present embodiment will be described. Is smaller than LMAX (that is, the maximum catalytic oxygen holding amount of the conventional apparatus). That is, since the target value (= HOSCy × １ ／) is smaller in the present embodiment than in the conventional device, the deviation of the target value toward the side larger than the optimum value can be made smaller than that in the conventional device.

Thus, in this embodiment, when the exhaust air-fuel ratio downstream of the catalyst is near stoichiometric and the exhaust air-fuel ratio upstream of the catalyst is rich, the exhaust air-fuel ratio downstream of the catalyst is near stoichiometric and The maximum value separately when the exhaust air-fuel ratio upstream of the catalyst is lean (when the exhaust air-fuel ratio downstream of the catalyst is near stoichiometric and the exhaust air-fuel ratio upstream of the catalyst is rich, the maximum amount of catalyst oxygen desorbed by the catalyst metal, When the exhaust air-fuel ratio downstream of the catalyst is near stoichiometric and the exhaust air-fuel ratio upstream of the catalyst is lean, the maximum catalytic oxygen absorption by the catalyst metal is calculated) and the target value is calculated based on the average of the two maximum values. since so as to calculation, the neighborhood near the exhaust air-fuel ratio is stoichiometric downstream of the catalyst by wide-range air-fuel ratio sensor and the catalyst downstream O ₂ sensor variations, or variations in the air-fuel ratio control of the catalyst upstream In addition, there is a difference in length between the section where the exhaust air-fuel ratio upstream of the catalyst is rich and the section where the exhaust air-fuel ratio downstream of the catalyst is near stoichiometric and the exhaust air-fuel ratio upstream of the catalyst is lean. However, it is possible to suppress the variation of the target value, thereby improving the air-fuel ratio control accuracy.

Next, the determination of the permission condition for calculating the maximum catalyst oxygen holding amount HOSCy by the catalyst metal (S 10 in FIG. 6).
22) will be described with reference to the flowchart of FIG.

The permission conditions are determined in steps S41 to S46 in FIG.
By checking the contents of HOSCy one by one, and permitting the calculation of HOSCy when all the items are satisfied,
If even one is not true, the calculation of HOSCy is prohibited. S41: Not in the low rotation speed range or the high rotation speed range; S42: Not in the low load range or the high load range; S43: After warm-up is completed; S44: Abnormality in the swing of the air-fuel ratio feedback correction coefficient α. No, S45: The catalyst is activated, S46: The number of times of shift deviation correction of the wide area air-fuel ratio sensor output is not equal to or greater than a predetermined value, when the calculation of HOSCy is permitted in S47, otherwise the flow proceeds to S48. The calculation of HOSCy is prohibited (permission flag = 0).

Whether the catalyst is activated is determined by comparing the catalyst temperature TCAT (detected by a catalyst temperature sensor not shown) with a predetermined value. That is, TC
When AT is less than a predetermined value (the catalyst is not active),
Since the oxygen storage capacity of the catalyst does not work, the process proceeds to S48. This is because when the catalyst is not in an active state, it is difficult for oxygen to be desorbed from the catalyst and oxygen to be absorbed into the catalyst. The sampling of the amount is prohibited and the variation of the maximum value is suppressed.

The shift deviation of the output of the wide-range air-fuel ratio sensor will be described with reference to FIG. 9. The output of the wide-range air-fuel ratio sensor upstream of the catalyst tends to shift toward the rich side or the lean side. The output of the O ₂ sensor downstream of the catalyst during the lambda control shows an abnormal change. Due to the influence of the shift of the output of the wide-range air-fuel ratio sensor to the rich side, the output of the O ₂ sensor becomes a predetermined value C or more (C> RSL) as shown in the figure (Case 1 and Case 3), Conversely, if the output of the O ₂ sensor falls below the predetermined value D (D <LSL) due to the shift shift of the output of the wide-range air-fuel ratio sensor to the lean side (Case 2 and Case 4), O ₍₂₎ The determination of the air-fuel ratio downstream of the catalyst based on the sensor output becomes inaccurate. Therefore, it is determined whether or not a shift error has occurred in the output of the wide-range air-fuel ratio sensor, and when a shift error has occurred, the shift error is corrected for the output of the wide-area air-fuel ratio sensor, so that the output of the wide-range air-fuel ratio sensor becomes rich. Even if there is a shift shift to the lean side, the air-fuel ratio determination downstream of the catalyst based on the output of the O ₂ sensor is performed with high accuracy.

The flowchart of FIG. 10 is for correcting a shift deviation occurring in the output of the wide area air-fuel ratio sensor upstream of the catalyst. In S51, the O ₂ sensor output VR downstream of the catalyst
O2, the wide area air-fuel ratio sensor output VFAF upstream of the catalyst is read. In S52, it is determined whether or not a predetermined time has elapsed since the VFAF became equal to or more than the predetermined value C. When a predetermined time has elapsed since the VFAF became equal to or higher than C, it is determined that the output of the wide-range air-fuel ratio sensor has shifted to the rich side, and S5
In step 3, a value obtained by subtracting the shift amount (fixed value) from the VFAF is set again as the VFAF. If the shift is likely to occur many times, there is a high possibility that the wide area air-fuel ratio sensor has a failure.
(Initial setting to 0 at startup) is incremented.

On the other hand, if the predetermined time has not elapsed since the VFAF became equal to or more than C, the process proceeds from S52 to S55, and it is determined whether the predetermined time has elapsed since the VFAF became equal to or less than D. When a predetermined time has elapsed since the VFAF became equal to or less than D, it is determined that the wide-range air-fuel ratio sensor output has shifted to the lean side, and the VFAF is determined in S56.
The value obtained by adding the shift amount (fixed value) to the above is set again as VFAF. In S57, similarly to S54, the shift deviation correction number counter CNT2 (initial setting to 0 at startup) is incremented.

The above two shift shift correction times (CNT
1, CNT2) are stored in a memory (RAM).

In FIG. 8, in S46, these two shift deviation correction times (CNT1, CNT2) are read from the memory. If any of these shift deviation correction times is equal to or more than a predetermined value, it is determined that the wide area air-fuel ratio sensor has a failure. Then, the process proceeds to S48 to prohibit the calculation of HOSCy.

As described above, when a shift shift occurs in the output of the wide-range air-fuel ratio sensor and the number of shift shift corrections exceeds a predetermined value, a failure of the wide-range air-fuel ratio sensor may be considered. By prohibiting the calculation, it is possible to suppress variations in the maximum values (the maximum amount of catalytic oxygen desorbed by the catalytic metal and the maximum amount of catalytic oxygen absorption).

In the embodiment, when the exhaust air-fuel ratio downstream of the catalyst is near the stoichiometric ratio and the exhaust air-fuel ratio upstream of the catalyst is rich, the amount of catalytic oxygen desorbed by the catalyst metal per operation cycle time is calculated as Insufficient oxygen (F
O2 × Q × t) is multiplied by a constant aR which determines the rate of desorption of oxygen from the catalyst metal, and when the exhaust air-fuel ratio downstream of the catalyst is near stoichiometric and the exhaust air-fuel ratio upstream of the catalyst is lean. The case where the amount of catalytic oxygen absorbed by the catalyst metal per operation cycle time is calculated by multiplying the excess oxygen amount (FO2 × Q × t) per operation cycle time by a constant aL which determines the rate of oxygen absorption of the catalyst metal. Although the description has been made, simply, both (the amount of catalytic oxygen desorbed by the catalytic metal per operation cycle time and the amount of catalytic oxygen absorbed by the catalytic metal per operation cycle time) may be set to the same fixed value (second value). Embodiment). In FIG. 6, “aR × FO2 × Q × t” in S28 and “aR” in S29
L × FO2 × Q × t ”is a fixed value having the same value. This is for the following reason. Variations in the wide-range air-fuel ratio sensor and the O ₂ sensor or variations in air-fuel ratio control are caused by a section where the exhaust air-fuel ratio downstream of the catalyst is near stoichiometric and the exhaust air-fuel ratio upstream of the catalyst is rich (t1 to t1 shown in FIG. 7). t2) and a section in which the exhaust air-fuel ratio downstream of the catalyst is near stoichiometric and the exhaust air-fuel ratio upstream of the catalyst is lean (section between t3 and t4 shown in FIG. 7). However, if only this difference in section length is expressed regardless of the operating conditions, the amount of catalytic oxygen desorbed by the catalytic metal per operation cycle time and the amount of catalytic oxygen absorbed by the catalytic metal per operation cycle time should be the same fixed value. Because it is good. However, it goes without saying that the fixed value is finally determined by matching.

The lower part of FIG. 7 shows this case. That is, exhaust air-fuel ratio downstream of the catalyst in this case is in the vicinity of the stoichiometric and the exhaust gas air-fuel ratio of the catalyst oxygen desorption amount HOSCR _n and catalyst downstream due to catalytic metal when the exhaust air-fuel ratio is rich catalyst upstream stoichiometric catalytic oxygen absorption amount HOSCL _n by the catalytic metal when the exhaust gas air-fuel ratio of there and the catalyst upstream in the vicinity of the lean will be increased at the same slope,
As shown, LMAX is larger than RMAX.

In the embodiment, the description has been given of the case where the HOSCy calculation permission condition excludes the low and high rotational speed ranges and the low and high load ranges. However, the present invention is not limited to this, and the HOSCy calculation is performed in these operation ranges. Permission may be considered. Similarly, the description has been given of the case where the permission condition does not include before the completion of the warm-up. However, if the catalyst works even in the low temperature range before the completion of the warm-up, the calculation of the HOSCy can be permitted even before the completion of the warm-up.

In the embodiment, FIG. 7 shows a case where both the maximum catalytic oxygen desorption amount RMAX by the catalytic metal and the maximum catalytic oxygen absorption amount LMAX by the catalytic metal can be sampled. However, these maximum values may not be sampled in some cases. For example, there are cases where the O ₂ sensor output always stays stoichiometric, or where only the stoichiometric and lean stays, and does not swing to rich (or where only the stoichiometric and rich does not swing to lean). In these cases, it is necessary to forcibly change the air-fuel ratio to rich or lean in order to enable the calculation of HOSCy. It is to be noted that the manner of forcibly increasing the air-fuel ratio between rich and lean is well known (for example, Japanese Patent Laid-Open No. 9-22201).
No. 0) and will not be described in detail.

In the embodiment, the case where the sampling of the maximum catalytic oxygen desorption amount and the maximum catalytic oxygen absorption amount is not permitted when the number of shift deviation corrections is equal to or more than a predetermined value has been described.
When the integrated value of the shift deviation correction value is equal to or larger than a predetermined value, sampling of the maximum amount of catalytic oxygen desorption and the maximum amount of catalytic oxygen absorption may not be permitted.

In the embodiment, the case where the catalyst having the oxygen holding ability contains at least two components, a component having a high rate of oxygen absorption or desorption of oxygen, and a component having a low rate of oxygen desorption are described. However, the present invention is not limited to this. It is needless to say that the present invention can also be applied to the above catalyst.

[Brief description of the drawings]

FIG. 1 is a control system diagram of an embodiment.

FIG. 2 is a waveform chart showing measurement results of air-fuel ratios before and after a catalyst when the air-fuel ratio of exhaust gas is switched from rich to lean.

FIG. 3 is a flowchart for explaining calculation of a catalyst holding oxygen amount and feedback control of the catalyst holding oxygen amount.

FIG. 4 is a characteristic diagram showing a relationship between the output of a wide area air-fuel ratio sensor and the oxygen concentration in excess and deficiency.

FIG. 5 is a diagram showing a table of excess and deficiency oxygen concentrations.

FIG. 6 is a flowchart for explaining the calculation of the maximum amount of retained catalyst oxygen by the catalyst metal.

FIG. 7 is a waveform chart showing a relationship between an O ₂ sensor output and two slice levels.

FIG. 8 is a flowchart for explaining determination of a permission condition.

FIG. 9 is a waveform diagram of the output of the O ₂ sensor downstream of the catalyst when a shift shift occurs in the output of the wide area air-fuel ratio sensor upstream of the catalyst.

FIG. 10 is a flowchart for explaining shift deviation correction.

FIG. 11 is a diagram corresponding to claims of the first invention.

FIG. 12 is a diagram corresponding to claims of the second invention.

[Explanation of symbols]

2 control unit 3 wide area air-fuel ratio sensor 10 catalyst 13 O ₂ sensor

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02D 45/00 312 F02D 45/00 312Z (72) Inventor Osamu Matsuno 2nd Takaracho, Kanagawa-ku, Yokohama-shi, Kanagawa Nissan 3G084 BA09 BA13 CA03 CA04 CA09 DA04 DA10 DA25 EA04 EA07 EA11 EB08 EB16 EB25 EC03 FA27 FA30 3G091 AB03 AB06 BA01 BA14 BA15 BA19 CB02 DA06 DB01 DB04 DB06 DB10 DC03 EA18 EA33 FA08 FB11 FA13 GB01W GB02Y GB04Y HA36 HA37 3G301 JA25 JA26 KA08 KA09 KA24 KA25 MA01 MA11 NA01 NA03 NA04 NA08 NB02 NB03 NB11 NC02 ND02 ND13 ND15 NE13 NE14 NE15 NE16 NE23 PD03A PD09A PD09Z PD12Z

Claims (9)

[Claims] 1. A catalyst having an oxygen holding capacity disposed in an exhaust passage of an engine, and based on an excess / deficiency oxygen amount per predetermined time upstream of the catalyst when an exhaust air-fuel ratio downstream of the catalyst is near stoichiometric. And a means for controlling the air-fuel ratio of the engine such that when the air-fuel ratio control condition is satisfied, the catalyst oxygen holding amount at that time becomes a target value. Means for setting the target value, means for calculating a catalyst oxygen desorption amount when the exhaust air-fuel ratio downstream of the catalyst is near stoichiometric and the exhaust air-fuel ratio upstream of the catalyst is rich, Means for calculating the amount of catalyst oxygen absorbed when the exhaust air-fuel ratio is near stoichiometric and the exhaust air-fuel ratio upstream of the catalyst is lean; and the exhaust air-fuel ratio downstream of the catalyst changes from stoichiometric to rich. Means for sampling the amount of catalytic oxygen desorbed as the maximum amount of catalytic oxygen desorbed, and sampling the amount of catalytic oxygen absorbed when the exhaust air-fuel ratio downstream of the catalyst changes from stoichiometric to lean as the maximum amount of catalytic oxygen absorbed An engine for calculating an average value of the two maximum catalytic oxygen desorption amounts and the maximum catalytic oxygen absorption amount; and a means for calculating the target value based on the average value. Exhaust purification equipment. 2. A catalyst disposed in an exhaust passage of an engine and having at least two components, a component having a high oxygen absorption or desorption rate and a component having a low oxygen absorption or desorption rate, and a catalyst downstream of the catalyst. Means for calculating the amount of catalyst oxygen retained by a component having a high rate of oxygen absorption or desorption based on the amount of oxygen in excess or deficiency per predetermined time upstream of the catalyst when the exhaust air-fuel ratio of the exhaust gas is near stoichiometric; When the control condition is satisfied, the engine is emptied such that the catalytic oxygen holding amount by the component having a high oxygen absorption or oxygen desorption speed at that time becomes a target value for only the component having a high oxygen absorption or oxygen desorption speed. Means for controlling a fuel ratio, wherein the means for setting the target value comprises: when the exhaust air-fuel ratio downstream of the catalyst is near stoichiometric and the exhaust air-fuel ratio upstream of the catalyst is rich, Means for calculating the amount of catalyst oxygen desorbed by a component having a high rate of oxygen absorption or oxygen desorption; and when the exhaust air-fuel ratio downstream of the catalyst is near stoichiometric and the exhaust air-fuel ratio upstream of the catalyst is lean, the oxygen Means for calculating the amount of catalyst oxygen absorbed by a component having a high rate of absorption or desorption of oxygen, and a means for calculating the amount of oxygen absorbed or desorbed when the exhaust air-fuel ratio downstream of the catalyst changes from stoichiometric to rich. Means for sampling the amount of catalytic oxygen desorbed as the maximum amount of catalytic oxygen desorbed by a component having a high rate of oxygen absorption or oxygen desorption, and the oxygen absorption or desorption when the exhaust air-fuel ratio downstream of the catalyst changes from stoichiometric to lean. Sample the amount of oxygen absorbed by the catalyst due to the component with a high rate of oxygen desorption as the maximum amount of catalyst oxygen absorbed by the component with a high rate of oxygen absorption or oxygen desorption. Means for calculating an average value of the maximum catalytic oxygen desorption amount and the maximum catalytic oxygen absorption amount, and means for calculating the target value based on the average value. apparatus. 3. The exhaust gas purifying apparatus for an engine according to claim 2, wherein the component having a high rate of oxygen absorption or oxygen desorption is a catalyst metal. 4. A component having a low rate of oxygen absorption or desorption of oxygen is an oxygen absorption aid.
An exhaust gas purifying apparatus for an engine according to Claim 1. 5. The means for calculating the amount of catalytic oxygen desorbed by a component having a high rate of oxygen absorption or desorption of oxygen is the amount of catalytic oxygen desorbed per predetermined time by a component having a high rate of oxygen absorption or desorption of oxygen. The means for integrating, and the means for calculating the amount of catalytic oxygen absorbed by the component having a high rate of oxygen absorption or oxygen desorption are the catalyst oxygen absorption per predetermined time by the component having a high rate of oxygen absorption or oxygen desorption. The exhaust gas purifying apparatus for an engine according to any one of claims 2 to 4, characterized in that it is means for integrating. 6. The catalyst oxygen desorption amount per predetermined time due to the component having a high oxygen absorption or oxygen desorption rate and the catalyst oxygen desorption amount per predetermined time due to the component having a high oxygen absorption or oxygen desorption speed are as follows. The exhaust gas purifying apparatus for an engine according to claim 5, wherein the values are the same fixed value. 7. The method according to claim 1, wherein the amount of desorbed catalyst oxygen per predetermined time by the component having a high rate of oxygen absorption or desorption is determined based on the amount of oxygen deficiency per predetermined time upstream of the catalyst. 6. The exhaust gas purifying apparatus for an engine according to claim 5, wherein an amount of catalyst oxygen absorbed per predetermined time by a component having a high separation speed is calculated based on an amount of excess oxygen per predetermined time upstream of the catalyst. 8. A sensor for detecting an excess or deficiency oxygen amount per predetermined time upstream of the catalyst, and means for correcting a shift shift occurring in the sensor output, wherein the number of times of shift shift correction or the correction value The sampling of the maximum catalytic oxygen desorption amount and the maximum catalytic oxygen absorption amount is not permitted when the integrated value is equal to or greater than a predetermined value.
The exhaust gas purifying apparatus for an engine according to any one of the above items 1 to 7. 9. The method according to claim 1, wherein sampling of the maximum catalytic oxygen desorption amount and the maximum catalytic oxygen absorption amount is not permitted when the catalyst is not in an active state. Engine exhaust purification device.